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United States Patent |
6,215,351
|
Le
,   et al.
|
April 10, 2001
|
Fuse-latch circuit
Abstract
A fuse-latch circuit in which, by use of a first and a second control
signal, which are staggered over time with respect to one another, fuse
information can be read from a fuse into a latch element and can be stored
in the latch element. Both control signals are in this case obtained from
only one global signal by a delay element.
Inventors:
|
Le; Thoai-Thai (Munchen, DE);
Schneider; Helmut (Munchen, DE)
|
Assignee:
|
Siemens Aktiengesellschaft (Munich, DE)
|
Appl. No.:
|
321174 |
Filed:
|
May 27, 1999 |
Foreign Application Priority Data
| May 27, 1998[DE] | 198 23 687 |
Current U.S. Class: |
327/525; 365/225.7 |
Intern'l Class: |
H01H 037/76; H01H 085/00 |
Field of Search: |
327/525
365/225.7
|
References Cited
U.S. Patent Documents
5566107 | Oct., 1996 | Gilliam | 365/200.
|
5619469 | Apr., 1997 | Joo | 365/225.
|
5640365 | Jun., 1997 | Imamiya et al. | 365/236.
|
5680360 | Oct., 1997 | Pilling et al. | 365/225.
|
Foreign Patent Documents |
19631130A1 | Feb., 1998 | DE.
| |
Primary Examiner: Cunningham; Terry D.
Assistant Examiner: Tra; Quan
Attorney, Agent or Firm: Lerner; Herbert L., Greenberg; Laurence A., Stemer; Werner H.
Claims
We claim:
1. A fuse-latch circuit for a fuse, comprising:
a first MOS transistor having a source-drain path, a gate and formed of a
first conductivity type;
a second MOS transistor having a source-drain path, a gate and formed of a
said first conductivity type, and the fuse provided in series between said
source-drain path of said first MOS transistor and said source-drain path
of said second MOS transistor;
a third MOS transistor having a source-drain path, a gate and formed of a
second conductivity type;
a latch element connected to said source-drain path of said second MOS
transistor and to a node between said source-drain path of said first MOS
transistor and said source-drain path of said third MOS transistor, said
gate of said third MOS transistor being connected to said gate of said
second MOS transistor and receiving only one first global initialization
control signal; and
a delay element connected to said gate said first MOS transistor, said
delay element receiving the first global initialization control signal and
generating a second local control signal being staggered over time with
respect to the first global initialization control signal, the second
local control signal being supplied to said gate of said first MOS
transistor, and the first global initialization control signal and the
second local control signal used for reading information corresponding to
a state of the fuse and said information stored in said latch element.
2. The fuse-latch circuit according to claim 1, wherein said delay element
is formed from transistors.
3. The fuse-latch circuit according to claim 2, including inverters
connected between said delay element and said first MOS transistor for
providing a delay.
4. A fuse-latch circuit, comprising:
a first MOS transistor having a source-drain path, a gate and formed of a
first conductivity type;
a second MOS transistor having a source-drain path, a gate and formed of a
said first conductivity type;
a fuse provided in series between said source-drain path of said first MOS
transistor and said source-drain path of said second MOS transistor;
a third MOS transistor having a source-drain path, a gate and formed of a
said second conductivity type;
a latch element connected to said source-drain path of said second MOS
transistor and to a node between said source-drain path of said first MOS
transistor and said source-drain path of said third MOS transistor, said
gate of said third MOS transistor being connected to said gate of said
second MOS transistor and receiving only one first global initialization
control signal; and
a delay element connected to said gate said first MOS transistor, said
delay element receiving the first global initialization control signal and
generating a second local control signal being staggered over time with
respect to the first global initialization control signal, the second
local control signal being supplied to said gate of said first MOS
transistor, and the first global initialization control signal and the
second local control signal used for reading information corresponding to
a state of said fuse and said information stored in said latch element.
5. The fuse-latch circuit according to claim 4, wherein said delay element
is formed from transistors.
6. The fuse-latch circuit according to claim 5, including inverters
connected between said delay element and said first MOS transistor for
providing a delay.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuse-latch circuit in which, by a first
and a second control signal, which are staggered over time with respect to
one another, fuse information (i.e. fuse is defective or intact) can be
read from a fuse into a latch element and can be stored in the latter.
In a fuse-latch circuit, it ought to be possible to store fuse information
for the operation of a semiconductor component, for example of a
semiconductor memory, after the fuse information has been read from the
fuse in the event of the supply voltage being switched on.
2. Summary of the Invention
It is accordingly an object of the invention to provide a fuse-latch
circuit which overcomes the above-mentioned disadvantages of the prior art
devices of this general type, which manages with only one global control
signal in order to reduce the outlay on global wiring and to preclude the
occurrence of propagation delay problems between the global control
signals with respect to one another.
With the foregoing and other objects in view there is provided, in
accordance with the invention, a fuse-latch circuit for a fuse, including:
a first MOS transistor having a source-drain path and formed of a
conductivity type;
a second MOS transistor having a source-drain path and formed of a
conductivity type that is the same as the first MOS transistor, and a fuse
is to be disposed between the source-drain path of the first MOS
transistor and the source-drain path of the second MOS transistor;
a latch element connected to the second MOS transistor; and
a delay element connected to the first MOS transistor, the delay element
receiving only one first global initialization control signal and
generating a second local control signal being staggered over time with
respect to the first global initialization control signal, the first
global initialization control signal and the second local control signal
used for reading information corresponding to a state of the fuse and the
information read from the fuse being stored in the latch element.
In the case of a fuse-latch circuit of the type mentioned in the
introduction, the object is achieved according to the invention by virtue
of the fact that, in addition to the first control signal, the second
control signal is also obtained from a global initialization signal by the
delay element.
In the fuse-latch circuit according to the invention, therefore, two
essential further measures are employed in addition to the existing
circuit:
(a) One of the control signals is obtained from the other, global control
signal by the time delay, for which purpose inverters can advantageously
be used.
(b) The fuse is connected to ground only after initialization via a switch,
for example an NMOS transistor, in order to prevent a parallel-path
current, which will be present in the case of an intact fuse, during
initialization.
Other features which are considered as characteristic for the invention are
set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a
fuse-latch circuit, it is nevertheless not intended to be limited to the
details shown, since various modifications and structural changes may be
made therein without departing from the spirit of the invention and within
the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however,
together with additional objects and advantages thereof will be best
understood from the following description of specific embodiments when
read in connection with the accompanying drawings.
BRIEF DESCRIPTIONS OF THE DRAWINGS
FIG. 1 is a diagrammatic, circuit diagram for elucidating a fuse-latch
circuit according to the invention; and
FIG. 2 is a circuit diagram for elucidating the fuse-latch circuit
according to the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In all the figures of the drawing, sub-features and integral parts that
correspond to one another bear the same reference symbol in each case.
Referring now to the figures of the drawings in detail and first,
particularly, to FIG. 2 thereof, there is shown a prior art fuse-latch
circuit containing a latch storage element 1 with a first inverter 2, and
a second inverter formed of a p-channel MOS transistor 3 and an n-channel
MOS transistor 4. The transistors 3, 4 are connected in series with an
n-channel MOS transistor 5, whose source is connected to ground. Gates of
the MOS transistors 3, 4 are connected together and connected to an output
of the inverter 2. In addition, an input of the inverter 2 is connected to
a node between the transistors 3, 4.
A fuse initialization signal FINIT having the profile shown in FIG. 2 is
fed to an input terminal 6 and is present at a gate of a p-channel MOS
transistor 7 and at a gate of the n-channel MOS transistor 5. In addition,
a fuse set signal FSET is fed to an input terminal 8, which is connected
to a gate of an n-channel MOS transistor 9. The transistors 7 and 9 are
connected in series with a fuse 10 and with a supply voltage.
In the event of initialization of the fuse-latch circuit, first of all the
initialization signal FINIT is fed to the input terminal 6, as a result of
which, as soon as this signal becomes "high" (logic "1"), the transistor 5
turns on, whereas the transistor 7 turns off. The transistor 9 is still
turned off at this point in time. Once the fuse set signal FSET at the
input terminal 8 becomes high, the transistor 9 turns on, with the result
that the fuse information of the fuse 10 can be written to the latch
element 1. After the fuse set signal FSET has fallen again, the transistor
9 turns off, with the result that the information remains written in the
latch element 1.
The existing fuse-latch circuit of FIG. 2 necessarily requires two global
control signals, namely the signals FINIT and FSET, which requires a
considerable outlay on global wiring and, in addition, makes it difficult
to prevent propagation delay problems of the two global control signals
with respect to one another during distribution across a chip.
In the fuse-latch circuit 1 as shown in FIG. 1 and according to the
invention, provision is made, in addition to the existing circuit of a
delay element containing a p-channel MOS transistor 14, an n-channel MOS
transistor 15 and an n-channel MOS transistor 17 (see in particular, the
section situated to the left of dashed lines 11). The transistors 14, 15
and 17 are connected in series between ground and a supply voltage. The
fuse initialization signal FINIT is fed to an input terminal 16 as well as
to the input terminal 6, from which fuse initialization signal a fuse set
signal FSET is obtained with the aid of the delay element formed of the
transistors 14, 15 and 17, the fuse set signal being fed to the gate of
the transistor 9 (as in FIG. 2). In this case, the additional n-channel
MOS transistor 15 effects a time delay t between the signals FINIT and
FSET, i.e. a low-high edge of the signal FINIT and a high-low edge of the
signal FSET.
During the initialization phase, the signal FINIT is set to logic "0"
("low"), as a result of which the transistor 7 is switched on and the
latch element 1 is preinitialized with logic "1" ("high"). The signal FSET
is at logic "1" during the initialization of the latch element 1. A
parallel-path current through an intact fuse 10 is prevented by the
transistor T5.
After the initialization, the signal FINIT changes from logic "0" ("low")
to logic "1" ("high"). On account of the delay element, formed of the
transistors T14, T15 and T17, the signal FSET remains at logic "1" for the
duration t. Since the transistor T5 is switched on, the fuse information
is written to the latch element 1 as follows:
(a) If the fuse 10 is intact, the input of the inverter 2 is pulled to
logic "0", as a result of which the latch element 1 is reset.
(b) If, on the other hand, the fuse 10 is defective (e.g. bombarded by
laser), then a logic "1" ("high") is stored in the latch element 1.
After the duration t, the signal FSET changes to low, as a result of which
the transistor 9 is switched off and the fuse is decoupled from the latch
element 1.
In contrast to the existing fuse-latch circuit of FIG. 2, the fuse 10 is
connected between the transistor 9 and the node between the transistors 4
and 5 in the case of the fuse-latch circuit according to the invention.
The effect achieved as a result of this is that no parallel-path current
flows during initialization of the circuit in the case of intact fuses.
If appropriate, it is also possible for two inverters 12, 13 to be
additionally provided for the purpose of delay, but there is not a need
for this since the delay can actually be "built" into the transistors 14,
15, 17 on their own.
Thus, the invention enables the necessary control signals to be generated
locally from only one global signal, with the result that it is possible
to attain significant advantages in respect of the saving for the global
wiring and the prevention of propagation delay problems of the global
control signals with respect to one another during distribution across a
chip.
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